1. Field of the Invention
The present invention relates to an asymmetric modular multilevel converter, and more particularly, to an apparatus and method for controlling an asymmetric modular multilevel converter, which allow numerous levels to be expressed according to a combination of modules each using a different voltage.
2. Discussion of Related Art
Generally, a modular multilevel converter (MMC) includes a plurality of sub-modules in which a power semiconductor circuit forms two output terminals, and the plurality of sub-modules are connected in series.
Each sub-module includes, for example, an energy storage unit and a power semiconductor.
The power semiconductor may be configured with a power semiconductor switch and a free-wheeling diode and may be implemented with an insulated gate bipolar transistor (IGBT), for example. Such a sub-module is configured with a so-called half bridge circuit, a full bridge circuit or the like for which a plurality of power semiconductors are connected to each other.
In addition, one of a voltage of the energy storage unit, a zero voltage, and an inverted voltage of the energy storage unit is shown between the two output terminals of the sub-module of the MMC.
In such a conventional technology, a problem that an enormously high circulating current is generated when voltages of modules are controlled to be different using a half bridge structure arises, and this can be completely resolved by control using a full bridge structure.
Therefore, technology development for new multilevel converter control is required.